Broadband Terminated Dipole Antenna for ALE

Funny you should mention this. I tested an antenna from a company who sold it on ebay some time ago. I couldnt understand why icicles kept forming around the transformer and load, but then ... heat! It wasn't a very good performer anyway, so i sent it back. After that experience I thought I should get one of those laser thermometers, but had forgotten about it until you mentioned it.

 

Good work, I hope to link up with you. I did a demo with the x108G radio (20 watts) and end fed Hybrid into the American Legion net last weekend - great signal reports. I should have the t2fd antenna hooked to a CODAN ALE radio this month.

73

de KZ3H

 

Thanks,

Thanks, but it sounds like you're doing all the work hi. That CODAN is a dream radio!
I just switched the configuration to sloping Vee, West & South. I'm hoping to catch some of the special ale Eclipse activity from NA.

73
de oh8stn

 

I own a CHA TD along with some other Chameleon antennas. The only Chameleon antenna I still use today is the F-Loop. All the other antennas following the 5:1 transformer model sit packed away in some corner. I tested for years but the efficiency was just bad. Recently I compared a 1/4 wave homebrew vertical for 20m with the cha hybrid mil whip plus extension using WSPR. Stunning how much more efficient my little $5 wire vertical was. Sure the Chameleon 5:1 typ antennas are sturdy and work for the most part without a tuner but i am not in a shtf scenario. And even if I ever have to deal with shtf, a bit of wire and coax and I am on the air. Don't get me wrong, Chameleon makes very well made equipment but the whole 5:1 stuff is just too inefficient and I can travel lighter and transmit more efficient with some linked dipole and a 6m fiberglass mast.

 

I'm a fan of the linked dipole/fiberglass mast solution as well (as I might have mentioned before; I tend to repeat myself in my old age.)

But the OP's point about ALE is valid. ALE presents a bit of a conundrum in the antenna system department, particularly for portable operations. I'm still pondering this one.

 

KM4DYX you are right for ALE it might work just fine. One can find some interesting information on 5:1 subject here: http://www.g8jnj.net/broadbandhfvertical.htm

 

Nice Page Chris. How much does the entire system weigh, & how long would it take a single person to set up? It looks very interesting but isn't it lacking the configuration options and portability in comparison to the BBTD or T2FD?

My goal is to use a single spiderbeam 12m mast for antenna support. The ground rods make the system easier to deploy, but introduces more weight for field use. I also would not like fiddling around trying to push metal rods into frozen ground (65°N) during the winter. Did you mean this as a fixed installation? I also noticed your transformer and the termination resistors for sale on your website. How about some pictures on your website?

Thanks for sharing.

73
Julian oh8stn

 

It is possible to have broadband antennas that are efficient.
The are not all "radiating dummy loads"
You don't see anyone complaining about how inefficient a terminated rhombic is.

For reference, here is some info on the Broadband Butterfly Terminated Dipole Antenna.
Commonly known as the "BBTD Antenna", it is useful for base or portable ALE applications.
It is an HF antenna using triangular elements that achieves 3 MHz to 30 MHz with a typical SWR of <1.5:1
The BBTD efficiency is better than a T2FD terminated folded dipole antenna, which is the military and commercial HF standard.
There are several different BBTD configuration alternatives, including pyramid, inverted-V, and bow-tie.







.

 

WB4ENE writes:
Military stns are "communicators", not "hams" or "broadcasters" the "important things" are different for each of these station personality types

I'm pulling one of my T2FD NEC models and will find the power loss in the resistor right now. Hams and Broadcasters get wrapped around the Tx power loss, but the Communicator looks at the drop in QRN levels, which improve their Rx ability. You can always bump up the Tx power, but its kinda hard to get the neighbor to unplug his fishtank heater!

Ok,got it:
131 foot long terminated dipole at 45 feet elevation:
spacing between the two wires that are vertically separated: 14 inches

load/terminating resistor in center of the top wire: 900 ohm
450 ohm transformer/feed
100 watts Transmit power to the source:

4Mhz: pwr in resistor causing icicles: 71.7W - 900 ohm resistor
swr: 3.6 : 1 at the 450 balun
5Mhz: pwr in resistor causing icicles: 65.0W
swr: 4.1 : 1
7MHz: pwr in resistor causing icicles: 66.5W
swr: 1.7 : 1
10Mhz: pwr in resistor causing icicles: 73.7W
swr: 2.3 : 1

change the load resistor to 450 ohms Tx pwr 100 watts

4Mhz: pwr in resistor causing icicles: 56.5W - 450 ohm resistor
swr: 3.5 : 1 at the 450 balun
5Mhz: pwr in resistor causing icicles: 55.8W
swr: 6 : 1
7MHz: pwr in resistor causing icicles: 78.3W
swr: 1.9 : 1
10Mhz: pwr in resistor causing icicles: 65.3W
swr: 3.2 : 1

Change the transformer to 600:50 ohm
and Load resistor to 450 ohms:
4Mhz: pwr in resistor causing icicles: 56.5W
swr: 2.7 : 1 at the 600 balun
5Mhz: pwr in resistor causing icicles: 55.8W swr: 4.6 : 1
7MHz: pwr in resistor causing icicles: 78.3W swr: 2.0 : 1
10Mhz: pwr in resistor causing icicles: 65.3W swr: 2.4 : 1

You can tune VSWR overall shape by swapping out what transformer ratio you use. So, have a 200/300/450/600 balun available. Sweep, swap, sweep




Ken WB4ENE

 

Would you expect any difference in performance with the resistor on top and the balun below?

 

For the standard BBTD antenna with the feedpoint about 30 feet above ground, there's +3dB radiation advantage to putting the (16:1 balun) feedpoint at the top .
On 7 MHz, for the Inverted-V Delta Wing configuration of BBTD antenna, there is approximately +4 to +6 dB ERP advantage to feeding it at the top, mainly due to ground losses.
As the overall height of the wires of the antenna is increased, there is somewhat less advantage to feeding it at the top.

But, for SWR, it doesn't matter much whether you feed it at the top or bottom.
You can lay the antenna on its side also.
It provides good broadband SWR anyway.